Adobe After Effects CS4 - Manual (Page 574)

568 USING AFTER EFFECTS CS4
Effects and animation presets
Last updated 12/21/2009
Using Selection Text values to differently affect subsets of text
You can differently affect only certain subsets of text particles by specifying Selection Text values. To open the Particle
Playground options dialog box, click Options at the top of the Particle Playground entry in the Effect Controls panel.
(This is the same place where you can specify the text used by the Grid or Cannon emitters.) Then enter text in one or
more of the Selection Text fields, and click OK. After doing this, you can then choose one of the Selection Text sets
from the Character menu under one of the Affects property groups. For example, you can make gravity only affect the
letter e by entering e in Selection Text 1 and then choosing Selection Text 1 in Gravity > Affects > Characters.
Note: The string matching is case-sensitive, and it does include punctuation marks and other symbols.
As with all text features, consider using this feature with symbol fonts, like wingdings.
Changing a particle over its lifespan
Some controls affect the particle from birth: Cannon, Grid, Layer Exploder, and Particle Exploder. Others affect the
particle after birth and over the course of its lifespan: Gravity, Repel, Wall, Persistent Property Mapper, and Ephemeral
Property Mapper. To have full control over particle movement and appearance, you must balance these controls.
For example, if you want to use the Cannon to shoot sparks that fade over time, it may seem that you need only animate
the Color control of the Cannon. However, using this method, you change only the color of each new particle as it’s
created. To control the color for the lifespan of particles, create a layer map and use one of the Property Mappers to
alter the color channels of the particles.
The following list covers common particle behavior and how you can influence it.
Speed At particle creation, particle velocity is set by the Cannon and the exploders; Grid particles have no initial
speed. After particle creation, use the Force control in the Gravity and Repel control groups. You can also influence
the speed of individual particles by using a layer map to set values for the Speed, Kinetic Friction, Force, and Mass
properties in the Property Mappers.
Direction At particle creation, the Cannon includes particle direction; the Layer Exploder and Particle Exploder send
new particles in all directions; and Grid particles have no initial direction. After particle creation, direction can be
influenced by the Direction control in the Gravity control group or by specifying a Boundary (mask) in the Wall
control group. You can also influence the direction of individual particles by using a layer map to set values for the
Gradient Force, X Speed, and Y Speed properties in the Property Mappers.
Area Use a Wall mask to contain particles to a different area or to remove all barriers. You can also restrict particles
to an area by using a layer map to set values for the Gradient Force property in the Property Mappers.
Appearance At particle creation, the Cannon, Grid, Layer Exploder, and Particle Exploder set particle size unless you
replace the default dots with a layer map. The Cannon and Grid set the initial color, while the Layer Exploder and
Particle Exploder take color from the exploded dot, layer, or character. The Options dialog box affects the initial
appearance of text. After particle creation, you can use the Property Mappers to set values for Red, Green, Blue, Scale,
Opacity, and Font Size.
Rotation At particle creation, the Cannon and Grid set no rotation; the Particle Exploder takes rotation from the
exploded dot, layer, or character. Use Auto-Orient Rotation to make particles rotate automatically along their
respective trajectories. For example, a particle can point up as it climbs an arc, and point down as it descends. Rotation
isn’t easily visible for a dot particle. It is easier to observe only when you replace the dot particle with text characters
or a layer. After particle creation, use a layer map to set values for the Angle, Angular Velocity, and Torque property
in the Property Mappers.
Note: The appearance and rotation of a layer map particle changes in relation to the original appearance and rotation
of the mapped layer. For example, if you replace the default dot particles with a movie of a spinning wheel, the spinning-
wheel particles appear to spin when no particle rotation is applied.